Fiber optic header with integrated power monitor

ABSTRACT

An optical header for coupling a light source to an optical fiber is disclosed. The header preferably includes a ceramic substrate that has a recess for a vertical cavity surface emitting laser (VCSEL), or alternatively an edge emitting laser. An optical fiber is preferably attached to a ceramic substrate and terminates at a light source. The end of the fiber is preferably cleaved or polished to an angle such that light entering the fiber from the light source is substantially reflected into the fiber. A reflective coating is placed on the cleaved end of the fiber thereby permitting a small percentage of light to radiate away from the fiber and toward an intensity detector. The light preferably travels to the detector through a transmission medium such as a prism or an optical-grade epoxy. The header is particularly useful when used in conjunction with multiple fibers simultaneously to form an optical fiber array. The header is also useful to house an optical receiver, or to form a bi-directional header suitable for fiber optic communications.

FIELD OF THE INVENTION

The present invention relates generally to fiber optic communications.More particularly, the invention relates to a header arrangement forcoupling light from a light source into an optical fiber, the headerincluding a monitor for tracking the intensity of the light.

BACKGROUND OF THE INVENTION

Communications systems employing optical fibers are well known in theart. These systems typically transmit data by using a light source, suchas a laser, to emit pulses of light onto a waveguide. The waveguide,often implemented as a glass fiber, transmits the light pulses to anoptical receiver that senses the pulses of light and provides acorresponding output signal (typically an electrical signal) to areceiving system.

Optical communications systems may span large geographic regions, orthey may be implemented within single electronic components. Recently,vertical cavity surface emitting lasers (VCSELs) have been recognized asbeing useful in small-scale communications systems. Indeed, it has beensuggested that optical systems utilizing VCSELs may eventually replacemany systems that currently rely upon copper wires to transmitelectrical data signals. The advantages of optical communicationssystems over electrical systems commonly include high bandwidth and lowsignal loss which often results as optical data signals travel throughthe length of the fiber. Moreover, several optical fibers may be bundledtogether in a "fiber array" to form a communications channel that iscapable of transmitting multiple signals simultaneously.

An important element of any optical communications system is a method ofcoupling light emanating from a light source into the waveguide.Typically, a laser light source is coupled into an optical fiber in a"header block" arrangement. The most commonly used form of header usesthe well-known "butt coupling" method shown in FIG. 1. "Butt coupling"involves positioning the laser so that light is directly emitted into anend of the optical fiber. Typically, a substrate made of silicon,ceramic or another material supports the laser and at least a portion ofthe optical fiber. The "butt coupling" method is particularly suited foruse with edge emitter lasers that emit photons in an elliptical pattern,with the vertical axis of the pattern being longer than the horizontalaxis.

A common practice is to cut a groove into the substrate to support theoptical fiber. Although the groove often prevents lateral movement ofthe fiber, it also typically increases the difficulty in aligning thefiber with the light source since the elliptical pattern of lightemanating from the edge emitter is substantially narrow in the lateraldirection. The grooves must therefore be precisely placed or elsesignificant amounts of light can be lost, thus degrading the transmittedoptical signals.

Often, the intensity of the light emitted by the laser is not constantover time.

For example, environmental effects such as temperature or humiditychanges can affect the performance of the laser. To compensate forvariations in laser output, it is frequently desirable to monitor theintensity of the light emitted by the laser. The intensity of the lightis proportional to the output power of the laser, and the stability ofthe laser can be greatly improved by using the monitoring signal asfeedback into the light source controls. This feedback signal isobtained by measuring the output intensity of the laser by a detectorsuch as a photodiode and providing this signal to a well-knownelectronic feedback circuit that provides a drive signal to the laser asshown in FIG. 1.

Typically, it is impractical to measure the direct output of the laser,since an intensity detector cannot be placed between the laser and theoptical fiber without significantly degrading the amount of lightimpinging upon the fiber. Many lasers, including edge emitting lasers,emit light at both the front and back ends of the lasing cavity,commonly called the front and back facets. The front facet is generallythe primary output of the laser, with substantially fewer photonsemanating from the back facet. Still, the light emanating from the backfacet can provide an input to an intensity monitor in a feedback system.Using the back facet as an input to an intensity monitor, however, oftenresults in two distinct disadvantages. First, the power output from theback facet is not always directly proportional to the light which entersthe fiber from the front facet, since the relative intensities of lightemanating from the front and back facets can vary over time. Moreover,VCSELs do not typically have a back facet. Therefore, it is notdesirable to use a VCSEL in a buttcoupling arrangement with a powermonitor.

U.S. Pat. No. 5,163,113, issued Nov. 10, 1992 to Paul Melman, which isincorporated herein by reference, generally discloses a second form of aheader block arrangement that includes an edge emitting laser configuredto provide light in a vertical direction. As can be seen in FIG. 2A, anuntreated optical fiber is cleaved at about a 45 degree angle, and thiscleave is positioned directly above an edge-emitting laser attached to asubmount block so that emitted light substantially impinges upon theinner face of the cleaved end of the fiber. Alternatively, anedge-emitting laser directs light horizontally toward a mirror, and themirror reflects light vertically toward the fiber as shown in FIG. 2B.Because the optical fiber is untreated, light from the laser issubstantially reflected by the cleaved end into the longitudinal axis ofthe fiber. This arrangement provides several advantages over thebutt-coupling method. Most notably, the header is suitable for use withvertically-emitting VCSEL lasers. Moreover, the cleaved fiber approachallows improved fiber/light source alignment over the butt-couplingapproach. However, this approach often exhibits a marked disadvantage inthat monitoring the output intensity of the laser light source isimpractical. Moreover, the elements required to implement this methodwith an edge emitter (namely the submount block in FIG. 2A or the mirrorstructure in FIG. 2B) are cumbersome to manufacture.

Accordingly, there exists a need for an optical header arrangement thatefficiently couples light from an emitter source into an optical fiberwhile providing a substantially accurate measure of the intensity of theemitted light. Moreover, there exists a need for such a header toincorporate VCSEL lasers, to handle bidirectional opticalcommunications, and to support arrays of fibers that are used incommunications systems. This header should contain minimal components tosimplify manufacturing.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, aheader arrangement for an optical communication system is provided whichefficiently couples light from a light source into an optical fiberwhile monitoring the output power of the light source.

In accordance with one aspect of the present invention, a headerarrangement is configured to accommodate vertical cavity surfaceemitting lasers (VCSELs) as light sources, and is suitable for use in afiber array.

Particularly, a preferred embodiment of the invention includes a headerblock that supports a VCSEL or edge-emitting laser which emits lightvertically toward an optical fiber. The end of the fiber is preferablyformed into an angle of approximately 45 degrees and suitably placed incontact with a partially reflective coating. Light from the lasertravels through the bottom surface of the optical fiber until the lightimpinges upon the inner side of the coated face of the fiber. Althoughthe coating reflects most of the light along the longitudinal axis ofthe fiber, a small portion of the light transmits through the coatingand into a transfer medium such as a glass prism. The medium transfersthe light to a detector that suitably measures the intensity of thelight and develops an output signal. Other embodiments of the inventionemploy alternate transfer media such as optical adhesives.

In accordance with a further aspect of the present invention, a headerdesign is proposed which may be efficiently manufactured, and which maybe conveniently coupled to a fiber array with a minimum of redundantparts.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The above and other objects, features and advantages of the presentinvention are hereinafter described in the following detaileddescription of illustrative embodiments to be read in conjunction withthe accompanying drawing figures, wherein like reference numerals areused to identify the same or similar parts in the similar views, and:

FIG. 1 is an exemplary cross-sectional view of a prior art header blockutilizing the "butt coupling" method;

FIG. 2A is an exemplary cross-sectional view of a prior art header blockutilizing an edge emitter submount block;

FIG. 2B is an exemplary cross-sectional view of a prior art header blockutilizing a micro-mirror to deflect light from an edge-emitting laserinto an optical fiber;

FIG. 3 is a cross-sectional view of a first exemplary embodiment of thepresent invention that includes a prism as a light transfer medium;

FIG. 4 is a cross-sectional view of a second exemplary embodiment of thepresent invention that includes a chamber filler as a light transfermedium;

FIG. 5 is a cross-sectional view of a third exemplary embodiment of thepresent invention that includes a chamber filler and a glass plate aslight transfer media;

FIG. 6A is a cross-sectional view of an exemplary embodiment of thepresent invention that includes an optical receiver;

FIG. 6B is a cross-sectional view of an exemplary embodiment of thepresent invention that includes an optical receiver and a mirror;

FIG. 7A is a top-down view of an exemplary embodiment of the presentinvention that is suited for bidirectional optical communication;

FIG. 7B is a cross-sectional view of an exemplary embodiment of thepresent invention that is suited for bidirectional opticalcommunication;

FIG. 8A is a side view of an exemplary embodiment of the invention usingan edge emitter laser;

FIG. 8B is a side view of a an embodiment using an edge emitter laser ina parallel alignment to the optical fiber.

FIG. 9 is a perspective view of an exemplary incomplete header block ofthe present invention as implemented in a fiber array; and

FIG. 10 is a perspective view of an exemplary header block of thepresent invention as implemented in a fiber array.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

1. A Fiber Optic Header

To simplify the description of the exemplary embodiments, spatial termssuch as "above" and "below" will be used. These terms refer to therelative positions of elements in the drawings. Persons skilled in theart, however, should recognize that the header arrangement disclosedherein could be rotated or turned in many ways. Thus, the terms "above"and "below" merely describe the relative positions of the headercomponents and should not be read as limiting the physical orientationof the invention.

Referring to FIG. 3, a preferred embodiment of the present inventionsuitably includes a header arrangement 30 and a substrate 100 configuredsupport the various elements of header 30, including an optical fiber101 which is supported above a light source 102. Substrate 100 may beformulated of any well-known substrate material, including plastics ormetals, and is preferably comprised of ceramic or silicon. Multiplesubstrate materials such as plastic and ceramic may be combined within asingle header arrangement.

FIG. 3 shows an exemplary support structure that includes a lower "base"substrate 100A configured to support light source 102, and a secondarysubstrate block 100B configured to support optical fiber 101. Althoughthese substrate components are shown as two separate elements, multiplesubstrate elements can be combined into a single structure. Similarly,additional substrate elements could be added. For example, it isfrequently useful to increase the height of substrate 100D (to the leftof the light source), particularly when hermetically sealing variousheader components together into an integral header structure. Substrate100B (which supports the fiber above the light source) is constructed ofany material suitable for use with the header arrangement. Moreover,optional upper substrate 100C may be configured to further supportoptical fiber 101. Upper substrate 100C may be comprised of the samematerial and of the same shape as the lower substrate elements.Alternatively, upper substrate 100C may comprise a glass plate coveringsome or all of header 30. In a preferred embodiment, grooves are etchedor cut by known procedures into substrate 100B to accept optical fiber101 and to prevent lateral movement of fiber 101 within its groove.

Header block 30 (shown in FIG. 3), and particularly substrate 100B, issuitably configured to support any type of optical fiber 101. Opticalfiber 101 may be comprised of any well-known optical glass or plastic,and may be suitably implemented in a single-mode, multi-mode, or anyother type of wellknown optical fiber. The outer jacket is suitablyremoved from the section of fiber 101 interfacing with header block. Forsimplicity, only the core of fiber 101 is shown in the figures. In thisregard and with momentary reference to FIG. 8, this core may includeseveral layers, e.g. an inner core 112 with a high index of refractionand a surrounding outer core 113 with a comparatively lower index ofrefraction. In the context of the present invention, it is generallydesirable to focus the bulk of emitted light upon inner core 112.

Referring again to FIG. 3, light source 102 is affixed to substrate 100,preferably (although not necessarily) through the use of a mountingstructure. This mounting structure is preferably a cavity or recess inwhich the light source may be placed (such as cavity 102A in FIG. 3) or,alternatively, an outcropping or mounting block (not shown) to which thelight source may be attached. In a preferred embodiment, light source102 is a VCSEL and substrate 100A includes a recessed area 102A. TheVCSEL is inserted into area 102A such that the emitting end of the VCSELpoints upward and out of the cavity. The VCSEL or other light source 102can preferably be secured within the substrate 100 with an optical gradeadhesive such as an epoxy, as described below. An exemplary light sourcesuitable for use in conjunction with the present invention may comprisea VCSEL laser chip available from the Microswitch division of HoneywellInc. of Richardson, Tex. In some embodiments, light source 102 is indirect contact with optical fiber 101. Preferably, however, a gap ispresent between light source 102 and fiber 101 to avoid scratching lightsource 102, as shown in FIGS. 3-5.

In an alternative embodiment, light source 102 may comprise an edgeemitting laser, affixed to substrate 100 through a mounting block (notshown) attached to the substrate. Since optical fiber 101 is physicallylocated above the light source and preferably directly above lightsource 102, the edge emitter may be advantageously situated such thatthe photons are emitted upwardly toward the fiber. Alternatively,photons can be emitted toward a mirror or focusing lens which issuitably configured to direct the photons upward to the fiber, similarto the prior art header shown in FIG. 2B. Other preferred embodimentsusing edge emitting lasers are discussed below.

End 101A of optical fiber 101 is preferably fashioned into a suitableangle by polishing, cleaving, or the like. The particular angle issuitably selected such that light from light source 102 willsubstantially impact upon the inner surface of the cleaved end 101A andwill substantially reflect along the longitudinal axis of the fiber, asshown in FIG. 3. For a more exhaustive discussion at the reflection oflight into a fiber, see U.S. Pat. No. 5,163,113, previously incorporatedby reference. When light source 102 is perpendicularly oriented withrespect to the axis of the fiber and below end 101A of fiber 101, theangle of the cleave is suitably in the range of 30 to 60 degrees, andmost preferably about 45 degrees, such that light moving vertically isdeflected by about a 45 degree angle to travel horizontally along thefiber axis. The particular angle selected may vary from implementationto implementation; however, the angle should preferably be selected toensure that the light entering optical fiber 101 is ultimately reflectedto travel along the longitudinal axis of optical fiber 101.

End 101A of fiber 101 is preferably placed in contact with a partiallyreflective coating 105 such as a dielectric or metal. As is known in theart, silver, gold, chromium and tin are particularly effectivereflectors that may be used as a coating. Alternatively, multiple layersof one or more dielectric materials may be deposited on fiber end 101A.In a preferred embodiment, end 101A is treated with a single layer ofgold or silver that is preferably mixed with chromium to form coating105. The thickness of coating 105 varies depending upon the particularimplementation, as discussed below, with a thicker coating causing morephotons to reflect. Optimally, coating 105 is such that approximately80-90%, and most preferably about 90-95% of the light reflects, andabout 1-20% (and preferably about 5-10%) of the light transmits throughthe coating 105.

Light intensity detector 103 is preferably located above fiber 101 andaligned to capture light emitted by light source 102 and transmittedthrough coaxing 105. This intensity detector (also called a "powermonitor" inasmuch as light intensity is proportional to the power of thelight) provides a signal 106 that is proportional to the number ofphotons impinging upon the sensor face. In a preferred embodiment,signal 106 is an electrical signal. An example of an intensity detectorsuitable for use in the context of the present invention may comprise aPIN photodetector, although virtually any light intensity detector thatis responsive to the type of light produced by light source 102 could beused.

Light that is not reflected by partially-reflective coating 105 issubstantially transmitted to detector 103 through a suitable medium.Although air may be a sufficient medium for some purposes as describedbelow, preferably a known glass element or prism such as element 104(see FIG. 3) is used. Prism 104 is suitably cut, polished, or otherwisefashioned to fit tightly against the cleaved face 101A of the fiber sothat minimal light escapes between fiber 101 and prism 104. As analternative to placing partially reflective coating 105 on end 101A ofoptical fiber 101, coating 105 may be placed on prism 104 whichcommunicates light to edge 101A of fiber 101 when prism 104 is mountedinto header block 30. Stated another way, the header generally functionssatisfactorily regardless of whether the coating is first placed oneither or both of prism 104 and fiber end 101A.

The header arrangement disclosed above efficiently couples light fromlight source 102 into optical fiber 101 and provides a power monitorsignal 106. When end 101A of optical fiber 101 is placed above lightsource 102, photons leaving the light source enter optical fiber 101from the bottom of end 101A. These photons travel upward through end101A until they reach reflective coating 105. The coating, incombination with the angle of fiber end 101A, causes a substantialportion of the photons to reflect along the length of fiber 101 towardan optical receiver (not shown). Most photons that are not reflected aretransmitted through coating 105, for example through conducting prism104 and into intensity detector 103.

As noted above, detector 103 provides an output signal 106 that is afunction of the number of photons impinging upon detector 103. Outputsignal 106 is preferably an electrical signal that can be used asfeedback to control electronics 107 which are suitably configured toproduce control signal 108 which, in turn, suitably adjusts light source102 to an optimal setting for producing optical signals to betransmitted on fiber 101. By using feedback from detector 103, thestability of light source 102 and, therefore, the performance of theoptical system is greatly enhanced.

Referring now to FIG. 4, a second embodiment of a header arrangement 40is shown. In this embodiment, an optical fiber 101 and a light source102 are suitably configured in a manner similar to that discussed abovein connection with FIG. 3. End 101A of fiber 101 is preferably cleavedor polished at an angle, and light from a light source 102 (which ispreferably a VCSEL, edge emitting laser, or other type of laser)radiates upward through fiber 101 where the light is partially reflectedand partially transmitted into fiber 101 by a reflective coating 105 onthe outer surface of the fiber end 101A. In this embodiment, however,the internal region 110 of header block 100, and most particularly theregion surrounding end 101A of the fiber, is suitably filled with aclear encasement material, for example an optical grade adhesive orepoxy such as EPO-TEK model 353ND epoxy available from the EpoxyTechnology Inc. corporation of Billerica, Mass. Alternatively, region110 could be filled with an ultravioletcured cured optical glue. Asshown in FIG. 4, a suitable barrier layer 109, which may be made fromplastic, metal or the like, may be configured to contain and secure theresin or other stabilizing material within region 110 by forming asubstantially hermetic seal between barrier 109 and header block 100. Inthis embodiment, light is transmitted from end 101A of the fiber to thephoto detector 103 via the stabilizing medium; consequently, the prismor other light conducting medium may be omitted, as desired.

In a further alternative embodiment, the epoxy in chamber 110 with maybe replaced air or other suitable gaseous medium; alternatively, chamber110 may be evacuated. In these embodiments, reflective coating 105 isoptional since the interface between the fiber and the gas/vacuum alongfiber edge 101A will reflect most of the light into fiber 101, with asmall amount of light nonetheless escaping fiber 101 and reachingphotodetector 103. In the exemplary embodiment of FIG. 4, however, anepoxy in chamber 110 is highly preferred over air or vacuum sincesubstantially more light reaches photodetector 103 in the presence ofthe epoxy. The epoxy is further advantageous in that it protects thevarious components of the header and holds the components together.Indeed, in an alternative embodiment, it is often desirable to fill thegaps in the header shown in FIG. 3 with an epoxy to prolong the life ofthe header.

FIG. 5 shows an example of combing the concepts illustrated in FIGS. 3and 4. Header 50 shown in FIG. 5 preferably includes an epoxy (or air)filled chamber 110 below a glass plate 111. The glass plate 111 may beanalogous in function to the prism shown in FIG. 3. Light transmittedthrough and 101A (with or without the use of a partially-reflectivecoating 105) is conducted through the epoxy-filled chamber 110 to glassplate 111, which then conducts light to detector 103.

FIG. 6A shows an exemplary header 60 suitable for use as a receiver inan optical communications system. Exemplary header 60 includes adetector 118 that receives optical signals transmitted along fiber 101and provides an output signal 120. As can be seen from FIG. 6A, fiber101 has an end 101A that is angled to deflect light toward detector 118.That is, light traveling on fiber 101 impacts upon reflective coating105 that is present upon fiber end 101A and is deflected downward towardthe optical detector 118. In an alternative embodiment, reflectivesurface 105 is implemented as a mirror or micromirror as shown in FIG.6B. By replacing optical receiver 118 with a light source such as aVCSEL or edge emitter, the header shown in FIG. 6B could also be used asa transmitter. Similarly, mirrors could be used in other embodiments ofthe invention, particularly in those embodiments that do not requirepower monitors, since mirrors are generally inexpensive and easy tomanufacture.

A more elaborate exemplary embodiment that is suitable for use in abi-directional communications system is shown in FIG. 7A. Abidirectional communications system includes a fiber 101 that is capableof transmitting optical signals in two directions. Such a systemrequires headers on each end of the fiber that are capable of bothtransmitting and receiving optical signals. Exemplary header system 70shown in FIG. 7A includes a light source 102 that provides opticalenergy to an angled end 101A of an optical fiber 101 as described in theembodiments associated with FIGS. 3, 4 and 5. A partially reflectivesurface 105 is preferably (but not necessarily) present between thefiber end 101A and a transmitting medium 104 such as a prism. As in theprevious embodiments, most of the light from light source 102 isreflected into fiber 101 and transmitted to a remote receiver. Some ofthe light, however, is transmitted through the coating 105 and medium104 to a power monitor 103 that is capable of providing an output signal(not shown) indicative of the intensity of light output by light source102. Also present in bi-directional header 70 is an optical receiver 118that is capable of receiving optical signals from a remote opticaltransmitter (not shown). When optical signals are received along fiber101, they encounter coating 105, which deflects a portion of the lightdownward toward light source 102. Light that is not reflected transmitsthrough coating 105 and medium 104 before reaching optical receiver 118.In preferred alternative embodiments, coating 105 is wavelengthselective such that light received from the remote optical transmittersubstantially transmits through the coating, yet light emanating fromlight source 102 is at least partially reflected, as discussed herein.Any wavelength selective coating such as single or multiple layers ofdielectric material could be used to implement coating 105. Becauseheader 70 includes apparatus for transmitting and for receiving opticalsignals, header 70 is suitable for use in a bidirectional opticalcommunications system. FIG. 7B shows another exemplary embodiment of abidirectional header that is preferably suited for use with a VCSELlight source. Similarly, an optical receiver 118 and/or a wavelengthsensitive coating 105 could be incorporated into other embodimentswithin the scope of the invention, including those embodiments disclosedin FIGS. 3-5.

2. Edge Emitting Lasers in a Fiber Optic Header

As noted above, photons emitted by an edge emitting laser form anelliptical pattern. Referring now to FIG. 8A, edge emitter 102 ispreferably configured such that the elongated axis 120 of the emittedlight pattern 122 is perpendicular to the longitudinal axis of opticalfiber 101 (i.e. axis 120 is orthogonal to the Z axis and parallel to theY axis of FIG. 8A). This perpendicular alignment is contrary toconventional wisdom (shown in FIG. 8B), which holds that light is bestcoupled from source 102 to inner core 112 when axis 120 is parallel tothe fiber. It has been observed, however, that outer core 101 of thefiber will refract photons toward the inner core 112 (as shown by arrowsA in FIG. 8A) due to the lens-like refracting properties of the barrierbetween outer core 113 and the surrounding medium (such as air orepoxy). This refraction has the effect of focusing photons from theouter reaches of ellipse 120 onto inner core 112. Stated another way,the bulk of the photons emitted by light source 102 are observed toreach inner core 112 even when axis 120 is situated perpendicular to thelongitudinal axis of the fiber as shown in FIG. 8A.

Referring again to FIG. 8A, an edge emitting laser 102 is arranged suchthat the longer axis of the elliptically-shaped emission pattern (whichruns parallel to the Y-axis in the figure) is perpendicular to thelongitudinal axis of the optical fiber (which comes out of the page asshown in the figure). As the photons impinge upon the glass of the outercore 113 of the fiber, most of the photons are inwardly refracted (seeArrows A) because the glass is more dense than the surrounding air orother material. The inward refraction causes the photons to be deflectedtoward inner core 112. Thus, edge emitter beam 122 is suitably matchedto optical fiber 101. This arrangement of the edge emitter laser may beincorporated into the various embodiments of the invention to improvethe coupling efficiency of the header.

The perpendicular arrangement of axis 120 provides an added advantageover a parallel arrangement in that the perpendicular arrangementsimplifies the alignment of light source 102 to optical fiber 101.Aligning the light source 102 to optical fiber 101 generally requiresextreme precision. With respect to the parallel arrangement, movement offiber 101 is generally restricted in the lateral direction (i.e. in theY direction shown in FIGS. 8A and 8B) by a groove cut into substrate100. When axis 120 is parallel to fiber 101 (as in FIG. 8B), alignmentis difficult because beam 122 has little margin for error in the Ydirection. By placing axis 120 perpendicular to fiber 101 as shown inFIG. 8A, however, a greater margin of error with regard to lateral (Ydirection) motion of the fiber is allowed. Therefore, a preferredexemplary method of aligning fiber 101 to light source 102 includesetching a groove in substrate 100 that is aligned with apreviously-placed light source 102, and then placing optical fiber 101within the groove. Aligning the end 101A of fiber 101 to the lightsource is preferably achieved by sliding fiber 101 within the groove cutin substrate 100 (i.e. by moving the fiber in the Z direction of FIG.8A). Thus, it is desirable to align edge emitter 102 such that thelonger axis 120 of the elliptical photon pattern is substantiallyperpendicular to the longitudinal axis of optical fiber 101 because suchalignment generally facilitates mechanical alignment of fiber 101 tolight source 102.

3. A Header for a Fiber Array

FIGS. 9 and 10 show perspective views of a header for a fiber array inaccordance with a preferred embodiment of the present invention. Theuppermost elements of the array (elements 103, 111, 116) have beenremoved in FIG. 9 to show the detail of the fiber/light sourceconnection. The header shown in these drawings suitably couples multiplelight source module 102 to multiple optical fibers 101, and preferablyincludes at least one intensity detector module 103 for monitoring thelight emitted by the respective light sources comprising module 102.

Referring now to FIG. 9, a parallel submount assembly 90 for fouroptical fibers 101 is shown. A base layer of the substrate 100preferably includes a metal trace 114 for each light source. Thesetraces suitably act as electrodes that provide drive currents to lightsources 102. Although the light sources 102 may receive electrical powerin any way, the traces 114 embedded in substrate 100 provide aconvenient, compact and easy-to-manufacture electrical conduit.

The base substrate in FIG. 9 also supports two secondary substrateblocks, one block (100A) surrounding the light sources (e.g. VCSEL lightsources) and another block (100b) supporting the optical fibers. Asdiscussed above, these substrate blocks may be implemented in any numberof ways. The substrate could be formed as a single block, for example,or could be divided into many sub-blocks. However, the light sources 102and optical fibers 101 are preferably supported by a single substratestructure 100 as shown.

The light sources 102 such as VCSELs or other laser light sources aresuitably embedded within cavities formed in the substrate 100A, and theangled ends of optical fibers 101 are aligned directly above theemitting ends of the light sources. The ends of fibers 101 arepreferably cleaved or polished to about 45 degree angles, but, asdiscussed above, the angle of the fiber depends upon the angle betweenthe impinging light and the longitudinal axis of the fibers. The ends offibers 101 are placed in contact with a partially reflective coating(not shown) so that most of the incoming light reflects along the lengthof fiber 101, but a portion transmits through fiber 101 to an intensitydetector (not shown in FIG. 9).

Referring now to FIG. 10, the upper layers of the fiber array header 100are shown. Light escaping from the end of fibers 101 is transmitted todetector 103 by a glass plate 111. The glass plate shown in the figurelies on top of the header block, but many alternative embodiments couldbe incorporated by one skilled in the art. For example, a triangularglass prism could be used in place of glass plate 111. The triangularprism aligns closely with the cleaved ends of fibers 101, and thereforetransmits light to detector 103 very effectively. In the embodimentshown, the gaps between the ends of optical fibers 102 and glass plate111 are preferably filled with an optical grade epoxy to aid in lighttransmission, similar to the arrangement disclosed in connection withFIG. 5.

Detector 103 receives light transmitted through glass plate 1 11 fromthe optical fibers 102 and provides a feedback signal (not shown) toindicate the relative power of the light received. The signal can betransmitted through metal traces 115 on glass plate 111, or through abonding wire connected to detector 103, or through any other knowncurrent conducting means. Detector 103 shown in FIG. 10 may be a singlephotodetector, or may comprise multiple photodetectors. If detector 103is a single photodetector, then the signal output will preferablyindicate the typical power of light reaching the detector from arepresentative light source 102. Alternatively, the output from detector103 could indicate the total power of all of the light reaching detector103 from all of the light sources 102 combined. If the detectorcomprises multiple photodetectors, then it is highly desirable to placean aperture 116 in the glass plate to prevent scattering of light fromone light source onto a photodetector associated with another lightsource. Aperture 116 is preferably a metallic coating with an openingthat is optically transparent.

In summary, an integrated header arrangement for a fiber opticcommunications system is disclosed. More particularly, a header forcoupling an optical fiber to a light source that includes an integratedpower monitor for tracking the intensity of light emanating from thesource is disclosed. The header arrangement is particularly well-suitedfor use with vertical cavity surface emitting lasers (VCSELs), as wellas in systems using arrays of multiple optical fibers.

The corresponding structures, materials, acts and equivalents of allelements in the claims below are intended to include any structure,material or acts for performing the functions in combination with otherclaimed elements as specifically claimed. The scope of the inventionshould be determined by the appended claims and their legal equivalents,rather than by the examples given above.

The claimed invention is:
 1. A header for use in an opticalcommunications system, the header comprising:a light source capable ofgenerating a light; and an optical fiber having a partially reflectiveend, the optical fiber being aligned such that the partially reflectiveend is located proximate to the light source; and a detector configuredto provide an output signal based upon transmitted light from the fiber;wherein the light source is aligned with the fiber such that the lightimpinges on an inner surface of said partially reflective end such thata first component of the light reflects substantially along alongitudinal axis of said optical fiber and a second component of thelight is transmitted through the partially reflective end to thedetector.
 2. A header of claim 1 wherein the partially reflective end isformed at an angle.
 3. A header of claim 2 wherein the angle issubstantially equal to 45 degrees.
 4. A header of claim 1 furthercomprising a transmitting medium, located between the partiallyreflective end of the optical fiber and the detector, for conducting thesecond component of light to the detector.
 5. The header of claim 4wherein the transmitting medium comprises glass.
 6. The header of claim4 wherein the emitting medium comprises adhesive.
 7. The header of claim6 wherein the adhesive is an epoxy.
 8. The header of claim 6 wherein theadhesive is an ultraviolet-cured optical glue.
 9. The header of claim 1further comprising feedback electronics capable of receiving the outputsignal from the detector and of providing a drive signal to the lightsource that is responsive to said output signal.
 10. The header of claim1 wherein said substrate comprises a recessed area to receive the lightsource.
 11. The header of claim 4 wherein said light source is avertical cavity surface emitting laser.
 12. The header of claim 4wherein said light source is an edge emitting laser.
 13. The header ofclaim 1 further comprising an optical receiver proximate to thepartially reflective end of the optical fiber, the optical receiverbeing capable of receiving optical signals from a remote opticaltransmitter through the partially reflective end.
 14. The header ofclaim 13 wherein the optical receiver provides an output communicationssignal that is responsive to the optical signals.
 15. The header ofclaim 2 further comprising an optical receiver proximate to thepartially reflective end of the optical fiber, the optical receiverbeing capable of receiving optical signals from a remote opticaltransmitter through the partially reflective end.
 16. The header ofclaim 4 further comprising an optical receiver proximate to thepartially reflective end of the optical fiber, the optical receiverbeing capable of receiving optical signals from a remote opticaltransmitter through the partially reflective end.
 17. The header ofclaim 16 wherein the optical receiver provides an output communicationssignal that is responsive to the optical signals.
 18. A method ofcoupling light emanating from a light source to an optical fiber, themethod comprising the steps of:providing the light source and a detectoron opposing sides of the optical fiber; aligning the optical fiber suchthat the light emanating from the light source impinges upon an innerreflective surface of the optical fiber, forming a first light componentthat is reflected substantially along the longitudinal axis of theoptical fiber and a second light component that is transmitted throughthe inner reflective surface; conducting the second light component tothe detector; and monitoring an output signal provided by the detectorthat is indicative of the intensity of the light emanating from thelight source.
 19. The method of claim 18 wherein the second lightcomponent is conducted to the detector by a prism.
 20. The method ofclaim 18 wherein the second light component is conducted to the detectorby an adhesive.
 21. The method of claim 20 wherein the adhesive is anoptical grade glue.
 22. The method of claim 21 wherein the optical gradeglue is an epoxy.
 23. The method of claim 18 wherein the second lightcomponent is conducted to the detector by air.
 24. The method of claim18 further comprising the step of providing a control signal to thelight source that is based upon the output signal provided by thedetector.
 25. A header block for an optical fiber array comprised of aplurality of optical fibers, each optical fiber having a partiallyreflective end forming a reflective inner surface, the header blockcomprising:a plurality of light sources, each light source beingassociated with one of said optical fibers; and at least one detector,each detector being associated with at least one light source; the atleast one detector is configured to provide an output signal based upontransmitted light from at least one light source; wherein each lightsource is aligned with one of said optical fibers such that light fromeach of said light sources impinges upon the inner reflective surface ofthe associated optical fiber, forming a first light component that isreflected substantially along a longitudinal axis of the optical fiberand a second light component that is transmitted through the innerreflective surface to the associated at least one detector.
 26. A headerblock of claim 25 further comprising at least one aperture between saidoptical fibers and said detectors for isolating said second lightcomponents to an associated detector.
 27. The header block of claim 25further comprising at least one glass element disposed between saidoptical fibers and said detectors for transmitting said second lightcomponents to said detectors.
 28. A header of claim 27 furthercomprising at least one aperture between said at least one glass elementand said detectors for isolating said second light components to anassociated at least one detector.
 29. The header of claim 27 whereinsaid glass element is a glass plate.
 30. The header block of claim 29further comprising an aperture disposed between said glass plate andsaid plurality of detectors for isolating said second light componentsto the associated detector.
 31. The header of claim 27 wherein saidglass element comprises a beveled surface substantially matched with theoptical fibers.
 32. A header for a fiber optic communications system,the header comprising:a light source; an optical fiber for receiving alight from the light source and for separating the light into a firstlight component that is substantially transmitted through the opticalfiber and a second light component that substantially passes through theoptical fiber; a medium for transmitting the second light component fromthe optical fiber; and a light detector for receiving the second lightcomponent from the medium and for providing an output signal based uponthe intensity of the second light component.
 33. The header of claim 32wherein the medium is a prism.
 34. The header of claim 33 wherein themedium is a glass plate.
 35. The header of claim 32 wherein the mediumis an adhesive.
 36. The header of claim 32 wherein the medium comprisesan adhesive portion and a glass portion.
 37. The header of claim 36wherein the glass portion includes a prism.